Mills for comminuting material



June 27, 1967 o. E. BICK MILLS FOR COMMINUTING MATERIAL s Sheets-Sheet 1' Filed April 29, 1965 Fla. 2.

FREQ UENCY--- INVENT DA v E.

June 27, 1967 p. E. BICK 3,327,954

MILLS FOR COMMINUTING MATERIAL Filed April 29, 1965 s Sheets-Sheet 2 INVENTOQ jam 11 E. Bnck Ev June 27, 1967 D. E. BICK MILLS FOR COMMINUTING MATERIAL Filed April 29, 1965 3 Sheets-Sheet 3 m w W. m m m m m\ w 5 mm w 5 x 2 w w \1 H m M 9 A4W F m Mqk-m ATTORNEY United States Patent 3,327,954 MILIS FUR COMMINUTING MATERIAL David Ewart Bick, Cheltenham, England, assignor to Dowty Rotol Limited Filed Apr. 29, 1965, Ser. No. 451,754 Claims priority, application Great Britain, May 1 ,1964, 18,199/ 64 9 Claims. (Cl. 241-175) This invention relates to mills for conrminuting material.

According to this invention, a mill for comminuting material comprises a liquid pulse generator, a liquid pulse receiver, a connecting means containing liquid by which liquid pulses can be transmitted from the generator to the receiver, a container for the material to be comminuted movable by the receiver under the action of each liquid pulse transmitted thereto, and at least one fluid compression device for returning the container towards a position from which it is movable by the receiver.

The fluid compression device, or each fluid compression device, may comprise another liquid pulse generator, another liquid pulse receiver, and another connecting means containing liquid by which liquid pulses can be transmitted from said other generator to said other receiver. Alternatively, the or each fluid compression device may comprise a liquid spring.

In the simplest form of the invention, the container is movable along a single directional axis by one liquid pulse receiver, and it is movable in the reverse direction along said axis by a fluid compression device.

In a more developed form of the invention, the container is movable by at least two fluid pulse receivers which act along diiierent directional axes and in sequence whereby a gyratory motion is imparted to the container, that is to say, the central point of the container turns about a fixed point Without the container itself rotating about its central point.

The mill desirably operates in a resonant condition in which the liquid displacement of the receiver exceeds the liquid displacement of the pulse transmitter, while the difference between said liquid displacements is absorbed by compression of the liquid in the connecting means. In this way it is possible to operate the mill efficiently with a pulse generator of smaller physical size than would be required for operation of the mill in a non-resonant condition.

The invention is illustrated by way of example in the accompanying drawings, of which:

FIGURE 1 is a side elevation of a ball mill in which a part of the mounting of the mill cylinder is broken away to show details,

FIGURE 2 is an end elevation,

FIGURE 3 is a diagram of the hydraulic operation and control of the mill,

FIGURE 4 is a longitudinal sectional diagram of a liquid pulse generator unit which operates the mill,

FIGURE 5 is a transverse section view on the line V-V of FIGURE 4, and 1 FIGURE 6 is a graph illustrating a method by which resonance of the system may be automatically controller,

FIGURE 7 is a side elevation of a ball mill forming another embodiment of the invention,

FIGURE 8 is a sectional view through the lower part of FIGURE 7 showing on an enlarged scale the mechanism for operating the mill, and

FIGURE 9 is a diagram showing the means for operation and control of the mill.

In the embodiment of FIGURES 1 and 2, a mill cylinder 11 forming a container for material to be comminuted is shown supported with clearance within a fixed mounting member 12 by sets of horizontal springs circuit for 13 and sets of vertical springs 14. The lower set of vertical springs are stronger than the upper set so as to support the cylinder centrally in the mounting member 12 when at rest. The mill cylinder 11 is actuated by four liquid pulse receivers which include hydraulic cylinders fixed in the mounting member 12, two of such cylinders 15 and 16 lying on a horizontal axis, and the other two such cylinders 17 and 18 lying on a vertical axis. The lower cylinder 18 is seen in FIGURE 3 but not in FIG- URE 2.

Pistons 19, 21, 22 and 23 are mounted in the hydraulic cylinders 15, 16, 17 and 18 respectively, and their projecting ends are pivotally connected by links 24, 25, 26 and 27 to flanges 28 which surround the mill cylinder 11. A projection 29 from the flanges 28 engages fixed guide blocks 31 to prevent the mill cylinder from turning about its central axis though permitting vibrating movement of the mill cylinder along the horizontal axis of the hydraulic cylinders 15 and 16 and along the vertical axis of the hydraulic cylinders 17 and 18.

The vibrating movement is imparted by liquid from a pulse generator unit, see FIGURES 4 and 5. The pulse generator unit has a cylinder block 32 in which a motor driven shaft 33 is continuously rotatable. Four parallel cylinder bores 34, 35, 36 and 37 disposed around the shafit 33 contain pistons 38, 39, 41 and 42 respectively. These pistons engage a swash plate 43 Which is connected to an extension 44 of the shaft 33 by a transverse pivot 45. The angle of the swash plate 43 is adjustable by a link 46 which pivotally connects the swashplate to an axially slidable rod 47 mounted in the shaft extension 44. The position of the rod 47 is controlled by a lever 48 which has a forked end 49 engaged between flanges 51 on the rod. Thelever 48 is pivoted intermediately at to a lug 52 in the cylinder block 32, while the other end of the lever 48 has a pin and lot connection 53 with a piston 54. The piston 54 engages a bore 55 in the cylinder block 32. A coaxial piston portion 56 engages a bore 57 of lesser diameter. The annular area of the piston 54 in the bore 55 is equal to the area of the piston portion 56 in the bore 57. The piston 54 is loaded by a spring 58 so that the lever 48 lifts the rod 47 from the shaft extension 44 to increase the angle of the swashplate 43, While the piston 54 is movable by the action of fluid pressure in the bores 55 and 57 to compress the spring 58 and decrease the angle of the swashplate. A bearing 59 interposed between the cylinder block 32 and a collar 61 on the shaft 33,

sustains the axial load on the shaft due to the load of the pistons 38, 39, 41 and 42 on the swashplate 43.

Referring now to FIGURE 3, it is seen that the connecting means is provided between cylinder bore 34 and the hydraulic cylinder 15 by a pipe 62. Similarly, pipe 63 connects the bore 35 and the cylinder 16, a pipe 64 connects the bore 36 and the cylinder 17, and a pipe 65 connects the bore 37 and the cylinder 18. The pipes 62, 63, 64 and 65 are of equal lengths and bore. Fluid pulses generated in the cylinders 34, 35, 36 and 37 are thus transmitted by the pipes to the respective cylinders 15, 16', 17 and 18. Since the pulses are generated sequentially in the cylinders 34-37 by rotation of the shaft 33 and the swashplate 43, a gyratory motion is imparted to the mill cylinder 11 by actuating movement of the pistons 19, 21, 22 and 23 in sequence, in which the central axis of the cylinder 11 rotates about the position which said central axis occupies when the cylinder is at rest.

A minimum positive pressure is maintained in the pipes and cylinders by a priming pump 66 which draws liquid from a reservoir 67 and which discharges into a delivery line 68, the pressure in which is controlled by a by-pass relief valve 69. The delivery line 68 is connected to each of the pipes 62, 63, 64 and 65 through a separate nonreturn valve 71.

The motion of the mill cylinder 11 is the resultant of linear movement of the pistons 19 and 21 along one axis and of linear movement of the pistons 22 and 23 along a perpendicular axis, both such movements being of different phase. It is desired that the mill cylinder 11 shall operate in a resonant condition, this condition being determined, inter alia, by the effective mass of the mill cylinder and its contents and by the resiliency of the columns of liquid in the pipes 62, 63 and 64, 65. In the resonant condition, the displacement of liquid in the hydraulic cylinders 15, 16, 17 and 18 exceeds that in the corresponding cylinder bores 34, 35, 36 and 37 of the liquid pulse generator.

The system may be tuned to resonance by means of variable capacity chambers 72, 73, 74 and 75 which are connected to the respective pipes 62, 63, 64 and 65. Pistons 76, 77, 78 and 79 are adjustable in the respective chambers 72, 73, 74 and 75 by means of screw-threaded piston rods 81, 82, 83 and 84 respectively. The lengths of the transmission pipes 62, 63, 64 and 65 and the positions at which the capacity chambers are connected are chosen to provide a maximum tuning effect by adjustment of the pistons 76, 77, 78 and 79. The capacity chambers may even be connected directly to the respective hydraulic cylinders 15, 16, 17 and 18.

The tuning of the four chambers may be effected simultaneously as shown by a gear motor 85 having parallel shafts 86, and 87 projecting from both ends of the motor casing. The shaft 86 has axially slidable driving connections 88 with the pistons 76 and 77, and the shaft 87 has axially slidable driving connections 88 with the pistons 78 and 79. The piston rods 81 and 84 are screw-threaded in one sense while the piston rods 82 and 83 are screwthreaded in the opposite sense. When the motor 85 operates with the shafts 86 and 87 turning in opposite directions, all four pistons will move axially in the same sense in the respective chambers.

Amplitude measuring devices are provided for controlling the motor 85, and for limiting the amplitude of movement of the millcylinder 11. The device for measuring amplitude in the direction of the axis of the cylinders and 16, includes fluid flow generating means formed by annular pumping chamber 88 between the cylinder 16 and piston 21, an inlet valve 89 receiving liquid from a low pressure pipe 91, and an outlet valve 92 discharging to a pressure signal pipe 93. This pipe 93 discharges through an adjustable restrictor 94 to the low pressure pipe 91 which is connected to the reservoir 67. An accumulator 95 connected to the pipe 93 smooths out pressure fluctuations in the signal pipe 93. The pressure in the pipe 93 is a function of the amplitude.

A similar device for measuring amplitude in the direction of the axis of the cylinders 17 and 18 includes an annular pump chamber 96, an inlet valve 97 connected to the pipe 91, an outlet valve 98 discharging to a second pressure signal pipe 99, an adjustable restrictor 101, and an accumulator 102. Both adjustable restrictors 94 and 101 are ganged together so as to be simultaneously variable by a single operating member as shown schematically at 103. The pipe 91 is extended to collect leakage from low pressure zones around the rods of the pistons 19, 21, 22 and 23. By this means, the use of high pressure sealing glands on the pistons is avoided.

The pressure signal pipes 93 and 99 are connected to chambers 104 and 105 at opposite ends of valve body 106 in which a valve spool 107 is mounted. The valve body includes a pressure port 108 connected to the delivery line 68 from the priming pump 66, and We return ports 109, 111 which are connected by low pressure pipe 91 to the reservoir 67. A supply port 112 spaced axially between the ports 108, 109 is connected to one port of the gear motor 85, while a second supply port 113 spaced axially between the ports 108, 110 is connected to the other port of the gear motor. The spool 107 is central by springs 114 and 115 at opposite ends, and is movable under a predominating pressure in the chamber 104 or the chamber 105 to control operation of the gear motor 85.

It will be seen that the initial setting of the pistons 76 and 77 is such that the capacity of the chambers 72 and 73 is less than the capacity of the chambers 74 and 75. The mill cylinder 11 will thus have a resonance characteristic in the direction of the axis of cylinders 15, 16 which follows the curve A in the graph of FIGURE 6 where amplitude and frequency are the co-ordinates. The resonance characteristic in the direction of the axis of cylinders 17 and 18 follows the curve B whose peak is seen to lie at a lower frequency than the peak of curve A. At the point where the curves A and B cross, the amplitudes are equal and the pressure signals in the pipes 93 and 99 leading to the chambers 104 and 105 respectively are equal, whereby the motor is inoperative.

If, on the other hand, the capacities of the chambers 72, 73, 74, 75 are less than are necessary for this balanced condition, the resonance curves will be shifted to the position A and B. At the required frequency i.e. the rotational speed of the pulse generator shaft 33 the A curve will intersect the frequency ordinate at a point a which is below the intersection point b of the B curve. The pressure signal in the chamber will therefore exceed that in the chamber 104, so that the valve spool 107 will shaft and admit fluid pressure to the port '113. The resulting operation of the motor '85 will be in the sense to cause the pistons 76, 77, 78 and 79 simultaneously to increase the capacities of the chambers 72, 73, 74 and 75, whereby the resonance curves are restored to the positions A and B. By similar reasoning it will follow that if the capacities of the chambers 72, 73, 74 and 75 exceed that necessary for balanced condition of the valve, the pressure signals will again operate the valve and motor 85 to reduce the capacities of the chambers. The initial relative adjustment of the ganged variable restrictors 94 and 101 is made to provide equal amplitudes of the mill cylinder 11 in both directions in the balanced condition of the valve 106, 107.

It will follow that if the inertial reaction of the charge in the mill cylinder changes during continued operation, the amplitude measuring devices will generate signals in the pipes 93 and 99 which act to restore the system to vibrations of equal amplitude in both directions. Furthermore, if the mill is of the continuous feed type, the amplitude measuring devices will sense any drift of the resonance curves A and B arising from a change in mass of the charge, and act similarly to restore the system.

The pressure signal pipes 93 and 99 are continued to connect with the bores 55 and 57 respectively whereby these pressures are additive in their controlling effect upon the piston '54 which controls the angle of the swashplate 43. By controlling the operating member 103 to vary the restrictors 94 and 101, the magnitude of the pressure signals acting on the piston 54 can be varied to limit the amplitude of the pressure pulses from the pulse generator, and thus limit the amplitudes of movement of the mill cylinder to a desired value.

In the embodiment of FIGURES 7, 8 and 9, a mill cylinder 121 is attached to a supporting structure 12-2 by a cantilever spring 123 which resists movement of the cylinder 121 equally in two mutually perpendicular directions. The cylinder in this example is shown supported on a vertical central axis, but it may equally be supported on a horizontal axis.

The pulse generator unit, hydraulic cylinders and pistons, and the capacity chambers are constructed as an assembly without connecting pipes. A pulse generator unit 124 similar to that described with reference to FIGURES 4 and 5 has a shaft 125 connected by a coupling 126 to an electric motor 127. The generator 124 has passages 128, 129, 131 and 132 leading directly from the cylinders in which the reciprocable pistons are mounted, to the interiors, of thick-walled chambers 133, 134, 135 and 136 which are fixed on a supporting base 137. Coaxial cylinders 138, 139 formed in the chambers 133, 134, respectively have pistons 141, 142 mounted therein. Coaxial cylinders 143, 144 formed in the chambers 135, 136, on an axis perpendicular to the axis of the cylinders 138, 139 have pistons 145, 146 respectively mounted therein. The several pistons 141, 142, 145 and 146 are each connected by a pivoted link 147 to an attachment point 148 within a skirt portion 149 of the mill cylinder 121.

The chambers 133, 134, 135 and 136 form cavity resona tors in which the displacement of the pistons 141, 142, 145 and 146 respectively exceeds that of the pulses generated in the passages 128, 129, 131 and 132. The difference between the displacements at the two positions in each chamber in accommodated by compression of liquid within the chamber, after the manner of a liquid spring. To avoid the use of high pressure piston glands, a drain pipe 151 is connected to a low pressure zone in each cylinder around the the piston therein. The liquid capacity of the chambers 133-136 may be maintained by a priming pump as in the previous embodiment.

The capacity of the chambers 133 and 134 may differ from that of the chambers 135 and 136 so that the resonance characteristics follow displaced but overlapping curves as in FIGURE 6. Instead of hydraulic devices for sensing the amplitudes of movement of the mill cylinder in mutually perpendicular directions, there are provided two accelerometers 152 and 153 which provide electrical signals of displacement in the wires 154, 155 and 156, 157 respectively. The wires 154, 155, 156 and 157 are connected into a control unit shown generally at 158, in which the signals from the accelerometers 152 and 153 are converted into direct current signals and the difference between them is fed by wires 1'59, 161 to an amplifier 162. This amplifier is connected by wires 163, 164 to a motor controller shown generally at 1-65, by which the speed of the electric motor 122 can be varied. It is arranged that a difference in the signals from the accelerometers 152 and 153 causes the motor controller 165 to alter the speed of the motor 122 in the sense of restoring the amplitudes of the mill cylinder 121 in the two directions towards equality, at which point the mill cylinder will be vibrating near peak resonance in both directions.

The accelerometer signals are also fed by the wires 154, 155 and 156,157 to a second control unit shown generally at 166, in which they are converted to direct current signals and their sum is fed by wires 167, 168 to an amplifier 169. This amplifier is connected -by wires 171, 172 to the coil 173 of an electromagnetically controlled valve 174 The valve 174 controls the connection of a fluid pressure line 175 and an exhaust line 176 alternatively to a supply line 177. The supply line 177 leads to a control cylinder 178 in which a piston 179 is mounted, this piston 179 being the equivalent of the piston 54 in FIGURE 4 in controlling the angle of the swashplate of the pulse generator 124. The signals from the accelerometers 152 and 153 are thus caused to act on the piston 179 to limit the amplitudes of movement of the mill cylinder to a desired value.

In the embodiment of FIGURES 7, 8 and 9, the mill cylinder 121 is actuated on both strokes along each axis of movement. In a modified arrangement the mill cylinder 121 may be actuated on one stroke only. This modification can be readily achieved by providing the pulse generator 124 with two cylinders and pistons only, supplying the respective passages 128 and 131. The passage 129 is closed whereby the chamber 134 constitutes the enclosure of an undamped liquid spring in which the liquid is compressed by inward movement of the piston 142 in the cylinder 139. Obviously, loss of liquid from the chamber 134 cannot be tolerated and accordingly a packing gland may be provided between the cylinder 139 and the piston 142. Alternatively, leakage may be permitted, while a device is provided for returning liquid lost through leakage at the end of the stroke when the chamber is at minimum pressure. The passage 132 is also closed and the chamber 136, cylinder 144 and piston 6 146 are also arranged to operate as an undamped liquid spring.

Whereas the describe-d embodiments of the invention have shown four piston and cylinder devices for actuating the mill cylinder, it is possible to employ three pulse generators and three pulse receivers for actuating the mill cylinder, in which both the generators and the receivers are arranged on axes which are mutually inclined at so as to form a three phase hydraulic power transmission which imparts a gyratory motion to the mill cylinder similar to that described.

I claim as my invention:

1. A mill for comminuting material comprising a liquid pulse generator, a liquid pulse receiver, a connecting means containing liquid by which liquid pulses producible by the liquid pulse generator are transmissible to the liquid pulse receiver, a container for the material to be comminuted, the liquid pulse receiver having a driving connection with the container whereby the container is movable under the action of each liquid pulse transmitted to the liquid pulse receiver, and at least one fluid compression device operable upon the container to return it towards a position from which it is movable by the liquid pulse receiver.

2. A mill according to claim 1, wherein each fluid compression device comprises another liquid pulse generator, another liquid pulse receiver, and another connecting means containing liquid by which liquid pulses are transmissible from said other generator to said other receiver.

3. A mill according to claim 1, having at least two liquid pulse generators with associated connecting means and liquid pulse receivers, said generators being operable in sequence by driving means to transmit liquid pulses through the respective connecting means to the respective liquid pulse receivers, and said receivers having connections with the container at different positions around the container at which positions said receivers are operable along different directional axes to impart a motion to the container in which movement the central point of the container is movable around a fixed point, the mill including locating means arranged to prevent the con tainer from turning about its central point.

4. A mill according to claim 3, wherein the liquid pulse generators are formed in a unit comprising cylinder bores having pistons therein, and a rotata'bly drivable shaft adapted to reciprocate the pistons in the cylinder bores and so transmit liquid pulses through the respective connecting means to the respective liquid pulse receivers.

5. A mill according to claim 4, including stroke-varying means for controlling the displacement of the pistons in the cylinder bores, and an amplitude measuring device responsive to movement of the container, said device producing a signal of amplitude which is operable on the stroke-varying means to determine a maximum amplitude limit to movement of the container.

6. A mill according to claim 5, wherein the amplitude measuring device comprises fluid flow generating means operable by movement of the container, and a restrictor connected between said generating means and low pressure, and wherein the stroke-varying means includes a piston which is movable in response to the fluid pressure across said restrictor. v

7. A mill according to claim 3, including two amplitude signalling devices responsive to movement of the container along the respective different directional axes, resonance determining means including adjustable members for varying the capacities of the connecting means associated with the liquid pulse receivers which act along different directional axes, the adjustable members being pre-set one in relation to the other whereby the container is movable in resonance along the different directional axes, the peak resonances occurring at different frequencies of movement back and forth along the respective axes,

resonance controlling means responsive to the difference between the signals produced by said amplitude signalling devices, said resonance controlling means being operable simulaneously on said adjustable members to adjust the frequencies at which said peak resonances occur whereby these peak resonance frequencies are maintained near the operating frequency of the container.

8. A mill according to claim 3, including two amplitude signalling devices responsive to movement of the container along the respective different directional axes, means determining the capacities of the connecting means associated with the liquid pulse receivers which act along different directional axes whereby the container is movable in resonance along the different directional axes, the peak resonances occurring at different frequencies of movement back and forth along the respective axes, a motor arranged to drive the liquid pulse generators, a motor speed controller, and resonance controlling means responsive to the difference between the signals produced by said amplitude signalling devices, said resonance controlling means being operable on the motor speed controller whereby the frequency at which the liquid pulse generators are driven by the motor is maintained near both peak resonance frequencies.

9. A mill for comminuting material comprising a unit having a number of cylinder bores in each of which a pulse generator piston is mounted, a rotatably drivable shaft adapted to reciprocate the pistons sequentially in the cylinder bores, a number of liquid-filled chambers each rigidly associated with said unit and having one of said cylinder bores in communication therewith, a pulsereceiver cylinder fixed to the chamber, a pulse-actuated piston mounted in each pulse-receiver cylinder, a container for material to be comminuted, said pulse-actuated pistons being arranged in driving connection with the container at spaced-apart positions around it so as to impart sequential actuating movement to the container in accordance With sequential actuation of the pulse-generator pistons caused by rotation of said shaft.

No references cited.

WILLIAM W. DYER, JR., Primary Examiner.

HARRY F. PEPPER, ]R., Examiner. 

1. A MILL FOR COMMINUTING MATERIAL COMPRISING A LIQUID PULSE GENERATOR, A LIQUID PULSE RECEIVER, A CONNECTING MEANS CONTAINING LIQUID BY WHICH LIQUID PULSES PRODUCIBLE BY THE LIQUID PULSE GENERATOR ARE TRANSMISSIBLE TO THE LIQUID PULSE RECEIVER, A CONTAINER FOR THE MATERIAL TO BE COMMINUTED, THE LIQUID PULSE RECEIVER HAVING A DRIVING CONNECTION WITH THE CONTAINER WHEREBY THE CONTAINER IS MOVABLE UNDER THE ACTION OF EACH LIQUID PULSE TRANSMITTED TO THE LIQUID PULSE RECEIVER, AND AT LEAST ONE FLUID COMPRESSION DEVICE OPERABLE UPON THE CONTAINER TO RETURN IT TOWARDS A POSITON FROM WHICH IT IS MOVABLE BY THE LIQUID PULSE RECEIVER. 